Drive device and method for moving a vehicle part

ABSTRACT

The invention relates to a process for adjusting a motor vehicle part between at least two positions and a drive device for executing this process. The motor vehicle part is driven by an electric motor, and a pulse signal is generated according to the rotary motion of the electric motor which is supplied to a control unit for controlling the electric motor, in which at certain instants the value for the current force acting on the motor vehicle part is determined from the pulse signal. This value of the force is used as the criteria in the decision whether the electric motor is to be turned off or reversed [or not]. Before connection of the electric motor to the motor vehicle part measurements are taken on the electric motor for determining the individual motor characteristics, the measured values determined in this way are used in the determination of the value of the action of force.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a process for adjusting a motor vehicle partbetween at least two positions, and a drive device for a motor vehiclepart which can be adjusted between at least two positions.

2. Description of the Related Art

DE 43 21 264 A1 discloses a generic process and generic drive device inwhich an electric motor drives a motor vehicle window pane. By means oftwo Hall sensors which are offset by 90 degrees and which interact witha magnet located on the motor shaft a signal is produced from which theinstantaneous period duration of a motor revolution and thus theinstantaneous motor rpm are determined at each time at which one suchsignal enters a control unit for controlling the motor. As soon as theinstantaneous rpm change resulting from the difference of two successiverpm measured values exceeds a stipulated threshold value the motor isreversed in order to release a possibly pinched article.

DE 195 11 581 A1 discloses a similar drive device in which the thresholdvalue is variably chosen depending on the position, and a memory forcertain positions of the adjustment path, and storing the speed changesampled in an earlier run between two adjacent positions in order tocompute the shut-off threshold for the speed from a function of positiondepending on the last currently determined position and the speed.

DE-OS 29 26 938 discloses acquiring the motor rpm in a sliding roofdrive at uniform time intervals, finding the differences of successivevalues, adding these differences to one another when they are largerthan a predetermined threshold value, and triggering the shut-off orreversal of the motor as soon as the added sum exceeds a predeterminedthreshold value.

DE 43 12 865 A1 discloses a drive device for a motor vehicle windowwhich samples the motor rpm by means of two Hall detectors, and, whichwhen a threshold is exceeded for the relative change of rpm, reversesthe motor. In doing so, the threshold value is continually re-computeddepending on the sampled motor voltage and the ambient temperature whichis determined by a temperature sensor on the motor. The status/operatingtimes of the motor are then considered in order to draw conclusionsabout the ambient temperature from the motor temperature.

DE 196 18 219 A1 discloses determining the rpm threshold or the rpmchange threshold of the motor, from which reversal of the motor takesplace, by determining the position-dependent rpm data of a reference runtaken place beforehand and depending on the position of the cover for asliding roof drive.

EP 0 422 388 A1 discloses pinching protection for an adjustable motorvehicle part in which the first derivative of the drive motor torque isadded over part of the range of motion of the adjustable motor vehiclepart, a boundary value for the sum being used to shut off the drivemotor.

U.S. Pat. No. 5,278,480 describes a learning program for a device foropening and closing a garage door.

DE 40 00 730 A1 discloses pinching protection for an adjustable motorvehicle part by the monitoring of the motor rpm or the first derivativeof the motor rpm such that pinching will be recognized. Thecharacteristics of the individually used motor, optionally withconsideration of the inherent heating of the motor, are determined byconnecting the motor to a completely assembled part and then exposingthe part to a defined load moment from which the motor rpm isdetermined. The disadvantage in this pinching protection is that onlyadaptation of the entire system comprising the motor characteristic, themotor temperature, and the resistance to movement of the adjustablemotor vehicle part is possible. This results in a certain amount ofinaccuracy in recognition of pinching.

The disadvantage in the above generic systems, which sample the rpm, isthat due to individual fluctuations of the characteristics of the motorsused, the assignment of the measured rpm to the corresponding motortorque, i.e. the corresponding force acting on the adjustable motorvehicle part, is subject to these random fluctuations; this results ininaccuracies in the determination of a case of pinching.

SUMMARY OF THE INVENTION

The object of this invention is to provide a drive device for a motorvehicle part which can be moved between at least two positions and aprocess for adjusting a movable motor vehicle part between at least twopositions, which will provide better accuracy in the determining whethera case of pinching has been encountered.

In this approach, there is an improvement when fluctuations in theindividual motor characteristic of the electric motor utilized can becompensated for such that an accurate determination of the motor torqueand thus of the force acting on the adjustable motor vehicle part can bedetermined, the result of which is that the accuracy in determiningwhether a case of pinching has occurred can be improved.

In a preferred embodiment, the instant input of each pulse signal on thecontrol unit is measured, from at least some of the previously measuredinstants one value at a time for the change of the motor rpm isdetermined, and from each value of the rpm change, when multiplied by aproportionality factor, a force change value is determined which is thenused when the value is determined for the instantaneous force acting onthe moveable motor vehicle part.

The proportionality factor is chosen as a function of the motorcharacteristic.

Preferably, the motor characteristic is determined for at least onemotor voltage before startup, i.e., without the driven motor vehiclepart is assembled, and at a fixed motor voltage, and more preferably twopairs of values of rpm and torque are measured.

Furthermore, the proportionality factor is preferably chosen as afunction of the motor temperature, with the motor temperature preferablybeing estimated by the ambient temperature and the duration of motoroperation being measured.

Two embodiments of the invention are detailed below using the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic of a drive device of one embodiment ofthe invention,

FIG. 2 sets forth a graphic representation of a sample time behavior ofthe period duration of a motor revolution,

FIG. 3 illustrates a schematic of another process embodiment of theinvention for determining a case of pinching, and

FIG. 4 shows a motor vehicle roof used for illustration of the processas shown in FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, an electric motor 10, which is a DC motor,drives via a shaft 12 a pinion 14 which engages two drive cables 16 thatare guided to be resistant to tension and compression. Between theelectric motor 10 and the pinion 14 there is optionally another wormgear pair which is not shown. The movable covers 54 of the sliding motorvehicle roof, currently constructed as a sliding and lifting roof orspoiler roof, are generally driven by means of these drive cables 16.The window raisers of a motor vehicle door often act via a cable drumand a smooth cable attached to the movable part, i.e. the window. It isnot relevant for the following discussion how the force is applied tothe movable motor vehicle part. However, for the sake of illustrationand clarity of this embodiment the driven cover 54 of a sliding andlifting roof is shown in FIG. 4.

A magnet wheel 18 with at least one south pole and one north pole ismounted torsionally firm on the shaft 12. Of course there can also beseveral poles, for example four north poles and four south poles, on themagnet wheel 18, by which the duration of the period of the signals isshortened accordingly. In the peripheral direction, offset by roughly 90degrees there are two Hall sensors 20, 22 disposed near the magnet wheel18 each of which deliver a pulse signal for each passage of the northand south pole of the magnet wheel 18 to a control unit 24. The controlunit 24 is provided with a microprocessor 36 and a memory 38 and whichreceives a signal for roughly each quarter revolution of the shaft 12.The period duration is determined from the interval of two successivesignals from the same sensor 20 and 22 and which are part of theinterval of one complete revolution of the shaft 12. Due to the 90degree arrangement of the two sensors 20, 22, the period duration iscomputed alternatingly from the time difference of the last two signalsfrom the sensor 20 and 22 such that for each quarter revolution a newvalue of the period duration is available. From this method ofdetermining the period duration, deviations from the exact 90 degreegeometry of the sensor arrangement have no effect on the periodduration, which would be the case when the period duration is determinedfrom the time difference between the last signal of one sensor and ofthe other sensor.

As a result of the phase shift of the signals of the two sensors 20, 22,the direction of rotation can also be determined. In addition, thecurrent position of the cover 54 can be determined from the signals ofthe Hall sensors 20, 22 by supplying the signals to a counter 40 whichis assigned to the control unit 24.

The direction of rotation of the electric motor 10 can be controlled bythe control unit 24 via two relays 26, 28 with reversing contacts 30,32. The rpm of the motor 10 will be controlled by pulse width modulationvia a transistor 34 which is triggered by the control unit 24.

From the instant of signal input from the Hall sensors 20 and 22, themicroprocessor 36 determines the instantaneous period duration of therevolution of the shaft 12 and thus of the electric motor 10. Thusapproximately for each quarter turn of the shaft 12 a measured value forthe period duration is available. To also ensure pinching protectionbetween these instants, estimated values for the period duration arecontinuously extrapolated in a fixed time reference, for example aftereach 1 ms, from preceding measured values of the period duration, forexample by the following formula

T*[k]=T[i]+k·(a1·T[i−1]+a2·T[i−2]+a3·T[i−3]  (1)

where a1, a2, a3 are parameters, i being an index which for each signalinput is incremented, i.e., for each quarter period, and k being therunning index of the fixed time reference which is reset to zero foreach newly measured value for the period duration. Instead of the lastfour measured values, more or fewer measured values can be considereddepending on the requirements, for example only the last two values areconsidered.

The parameters a1, a2, a3 model the entire system of the drive device,i.e. the motor 10, the force transmission components and the cover 54,and are determined by the spring stiffness, damping and friction of theentire system. This yields bandpass action with the property thatportions of the period time behavior caused by vibrations are evaluatedmore weakly than those originating from a case of pinching. FIG. 2schematically shows the sample time behavior of the measured perioddurations T and the period durations T* which have been estimatedtherefrom. The broken-line curve represents the true behavior of theperiod duration.

From the estimated values for the period duration, which have beendetermined in this manner, the motor rpm change at time [k] relative tothe preceding instant [k−1] is estimated, with a motor voltage filterand a path profile filter being used to eliminate the effects of themotor voltage and the position at which the movable motor vehicle part,i.e. the cover, is in fact located, the following formula being used:

ΔN*[k]=(T*[k]−T*[k−1])/(T*[k])² −Vu(Um[k])−Vr(x[k])  (2)

Um[k] is the motor voltage at time [k], Vu is the motor voltage filterwhich simulates the relationship between the rpm and the motor voltagewhich has been received by the control unit 24, ×[k] is the position ofthe cover at time [k], and Vr is a path profile filter which simulatesthe relationship between the motor rpm and the position of the cover.

The motor voltage filter Vu simulates the dynamic behavior of the motorfor voltage changes. Preferably, the motor voltage filter Vu is made asa lowpass filter with a time constant which is equal to the motor timeconstant. The time constant is dependent on the operating situation,i.e. on the opening or closing of the cover 54 in the sliding orlowering direction, and is dependent on the magnitude of the voltagechange.

The path profile filter Vr is automatically determined by a learning runafter the drive device is installed. By doing this, multiple adaptationsto altered operating conditions, i.e., due to wear, during the servicelife of the system is possible within certain intervals. Further,instead of an individual learning run, statistical averages determinedfor several (for example 50) learning runs can be used for data recoveryfor the path profile filter. The position of the cover 54 is, asmentioned above, determined from the pulse signals of the Hall sensors20, 22 which are summed up by means of the counter 40.

The determination as to whether a case of pinching is present or not ismade using the following formula:

Σ(Vf·ΔN*[k])=Σ(ΔF[k])>Fmax   (3)

The estimated rpm changes ΔN*[k] are compared to a fixed, time-constantlower boundary. As soon as the estimated run changes exceed this lowerboundary, they are each multiplied by a proportionality factor Vf whichreproduces the slope of the motor characteristic of the electric motor10 (torque over rpm). At a constant motor voltage and motor temperaturethe slope is roughly constant, but for each electric motor 10 it isindividually different. To eliminate these effects, a temperature sensorsamples the ambient temperature and the motor temperature is determinedvia the determination of the operating duration. As an alternative, theambient temperature can also be directly determined by a temperaturesensor on the electric motor 10. On the other hand, for each electricmotor 10 before assembling with the cover 54, and within the frameworkof the final production check at a constant motor voltage, two pairs ofvalues for rpm and torque are determined and stored in a memory 38. Fromthese measured values, the increase of the motor characteristic isdetermined, from which the proportionality factor Vf is computed.

The product of ΔN*[k] and Vf corresponds to the change ΔF[k] of theforce acting on the displacement motion of the cover 54 at time [k]relative to the instant [k - 1].

The values of ΔF[k] are added up as long as the values of ΔN*[k] areabove the fixed lower boundary. As soon as two successive ΔN*[k] valuesare again below the fixed lower boundary, the sum is set to zero. If theΔN*[k] value exceeds a fixed upper boundary, in place of this ΔN*[k]only the value of the upper boundary is included in the sum. This isdone to eliminate, as much as possible, the effects of vibrations whichlead to brief periodic peaks of the rpm change upon the recognition of ainstance of pinching. This upper boundary can be chosen to be constantin the simplest case. However, in order to increase the accuracy oftriggering, the upper limit can also be chosen differently in timedepending on the currently determined rpm change, for example in themanner that the upper limit is raised as the current rpm change rises.

As soon as the sum of ΔF[k] exceeds a maximum allowable pinching forceFmax, the control unit 24 by triggering the relays 26, 28 via theswitches 30, 32 initiates reversal of the electric motor 10 in order toagain immediately release the pinched article or the pinched body part.

Due to the above described extrapolation of the period durations, thepinching protection is also active between the two measured values ofthe period duration at fixed instants, in which case pinching can berecognized earlier, i.e. at a lower pinching force; which betterprevents damage or injuries and thus increases the safety of the drivedevice.

To further reduce the probability of faulty activation when vibrationalforces occur, spectral analysis of the rpm changes determined within acertain time window up to the instant of the analysis can be undertaken.When certain spectral characteristics occur, especially when a clearlypronounced peak occurs which is not in the spectral range typical forcases of pinching, triggering is prevented even if the threshold Fmax isexceeded.

FIG. 3 schematically shows a second embodiment of the invention. Themajor difference from the above described first embodiment is thatparallel and independent of the extrapolation of the measured perioddurations at certain times and independent of the determination ofestimated values for the force acting on the adjustable motor vehiclepart in a first computation 50, a second computation 52 is carried outwith its own set of parameters and with a different scanning rate whichdelivers the value for the instantaneous action of the force. For thedecision whether the motor is to be turned off or reversed, the resultsof the two computations are considered. This results from the followingconsiderations.

The stiffness of the entire system comprises the stiffness of thesliding and lifting roof mechanism, of the pinched body, and of themotor vehicle body. On the one hand, the stiffness of the pinched bodydepends on the type of body, also, the stiffness of the body dependslargely on the location at which the body is pinched. This appliesespecially in the lowering motion of the cover 54 from a raisedposition, see FIG. 4. If, in doing so, a body 56 is pinched in the areaof the middle of the roof (indicated in FIG. 4 at 58), the effect on theentire system based on the possible deflection of the rear edge of thecover is much milder than for pinching in the edge area (indicated inFIG. 4 at 60).

The scanning rate is hereinafter defined as the interval of the instantsat which the value for the instantaneous action of the force isdetermined. If the system is working with a single fixed scanning rate,the set of parameters of the computation, especially the thresholdvalues or the boundary values, and the selected scanning rate can beoptimized only for a single stiffness of the entire system, but inpractice, depending on the type and location of the pinched body, adifference in stiffness of the entire system can be decisive.

By carrying out a second parallel computation 52, it is possible tooptimize this second computation 52 for another stiffness through thecorresponding choice of the computation parameters and the scanning rateunderlying the computation, i.e. the choice of the instants at which anew value of the instantaneous action of force is computed.

The second computation 52 is preferably optimized to determine slowchanges of the action of force, i.e. small stiffness, while the firstcomputation 50 is optimized to determine fast changes of the action offorce, i.e. high stiffness.

Generally, in the secondary computation 52 it is not necessary toextrapolate the measured values of the period duration, however,depending on the relevant stiffness range, that is in a case after inputof a new measured value or only after each n-th input of the measuredvalue, the computation 52 of the new value of the instantaneous actionof force is done. Basically, and if necessary, the second computation 52can use an extrapolation algorithm, where the extrapolation instants arechosen at a greater interval than in the first computation 50.

As shown in FIG. 3, in the rpm determination stage 62 is determined fromthe input values period duration T, the motor voltage, the coverposition x, and the motor temperature according to the aforementionedformulas (1) and (2) with the first (higher) scanning rate, i.e. at themeasurement instants [i] and the extrapolation instants [k], the currentrpm change ΔN* or the current rpm N* (this results from N*[k]=1/T*[k]-Vu(Um[k]) - Vr(x[k]; instead of [k], there can also be [i]).Furthermore, the motor temperature, when determining the rpm in theconversion from the change in rpm to the change in force, is taken intoaccount according to equation (3). The first scanning rate is chosensuch that it is optimum for the determination of cases of pinching whenthe highest system stiffness is to be expected. The rpm determinationstage 62 is used jointly by the first computation 50 and the secondcomputation 52.

In the first computation 50, it is ascertained from the rpm change ΔN*by means of the formula (3) in the aforementioned manner using the firstvalue for the fixed lower boundary, the first value for the fixed upperboundary, and the first value for the threshold value Fmax at theinstants which have been established by the first scanning rate, i.e.the extrapolation instants [k], whether the instantaneous action of theforce exceeds this first threshold value Fmax. The values of this firstparameter set are optimized for the determination of cases of pinchingwhen the largest system stiffness is to be expected.

In the second computation 52, the scanning rate is chosen such that itis optimum for determination of cases of pinching when the lowest systemstiffness are to be expected. This second scanning rate can be chosenfor example such that only each fourth measured value of the periodduration T is considered. In this situation, the second computation isperformed only for each fourth signal input from the Hall sensors 20,22, i.e. only each fourth rpm N[i] which is determined by the stage 62and which goes back to the measured period duration T is considered inthe scanning stage indicated at 66 in FIG. 4 (indicated in FIG. 4 by 66)and which goes back to the measured period duration T. The rpm N*[k]which has been determined from the extrapolated period durations T* areof course ignored. The second computation 52 is therefore carried outonly at each fourth instant [i].

Initially, the change of rpm ΔN[i] is determined relative to the lastmeasured value. Then, analogously, by means of the equation (3) using asecond value for the fixed lower boundary, a second value for the fixedupper boundary, and a second value for the threshold value Fmax, it isestablished whether the instantaneous action of force exceeds thissecond threshold value Fmax. The values of this second parameter set areoptimized for determination of cases of pinching when the smallestsystem stiffness is to be expected.

For the determination as to whether there is a case of pinching, i.e.the motor is to be turned off or reversed, the results of the first andthe second computation are logically combined with one another in thelogic stage 64. In the simplest case, this is an OR operation. Thereforein that situation, the motor is turned off or reversed when one of thetwo computations indicates a case of pinching. This decision is made ateach instant at which the first computation 50 delivers a new result.Since new results of the second computation 52 are present much morerarely, the last result of the second computation 52 is supplied to thelogic stage 64.

Both fast and subtle changes of the action of the forces can beoptimally determined by the combination of the results of the twocomputations 52, 54.

What is claimed is:
 1. A process for displacing a motor vehicle partbetween at least two positions comprising the steps of: prior toconnection of an electric motor to the motor vehicle part, takingmeasurements on the electric motor for determining an individual motorcharacteristic, driving the motor vehicle part with the electric motor,generating a pulse signal according to rotary motion of the electricmotor, inputting said signal to a control unit for controlling theelectric motor, determining a value of a current force acting on themotor vehicle part at certain instants from the generated pulse signal,and the value of the determined individual motor characteristic, andusing the determined value of the current force as a criteria indetermining whether the electric motor is turned off or reversed. 2.Process as set forth in claim 1, comprising the further steps ofcalculating a current force change value (<F[k]), the instant each pulsesignal is inputted to the control unit, from a previously determinedvalue of the current force by determining a respective rpm change valuewhich is indicative of a change of the motor rpm (<N*[k]), and bymultiplying the change value with a proportionality factor (Vf) todetermine an instantaneous current force acting on the motor vehiclepart.
 3. Process as set forth in claim 2, wherein the proportionalityfactor (Vf) is selected as a function of the motor characteristic. 4.Process as set forth in claim 3, wherein the motor characteristic isdetermined by measuring two pairs of values of motor rpm and motortorque at a fixed motor voltage.
 5. Process as set forth in claim 2,wherein the proportionality factor is chosen as a function of motortemperature.
 6. Process as set forth in claim 5, wherein the motortemperature is estimated from ambient temperature and duration ofoperation of the electric motor.
 7. Process as set forth in claim 2,wherein the values of the force change are summed when an estimated rpmchange exceeds a lower threshold value.
 8. Process as set forth in claim7, wherein, when the estimated rpm change (<N*[k]) exceeds an upperthreshold value, the upper threshold value replaces the estimated rpmchange in the summation of the force change value (<F[k]).
 9. Process asset forth in claim 8, wherein the upper threshold value is selected as afunction of at least some of recently determined values of the estimatedrpm change (<N*[k]).
 10. Process as set forth in claim 2, wherein thevalue for the instantaneous current force acting on the motor vehiclepart is determined between two pulse signal input instants at certainextrapolated instants.
 11. Process as set forth in claim 10, whereinupon inputting of a new pulse signal, a current period duration (T[i])of motor rotation is determined from the difference between the newpulse signal and at least one earlier pulse signal measured value, themeasured value of the current period duration (T[i]) of the motorrevolution is determined such that, at each extrapolation instant ([k]),an estimate of the current period duration (T* [k]) is determined fromat least one previously measured period duration (T[i-1], T[i-2],(T[i-3]) and the estimated period durations are determined from theestimated rpm change (<N*[k]).
 12. Process as set forth in claim 1,wherein the motor is turned off or reversed by the control unit as soonas the value of the current force acting on the motor vehicle partexceeds a predetermined trigger threshold.
 13. A drive device for amotor vehicle part which can be moved between at least two positions,comprising: an electric motor for driving the motor vehicle part, meansfor producing a pulse signal according to rotary motion of the motor, acontrol unit for receiving the pulse signal and for controlling theelectric motor, wherein the control unit is adapted to determine, at acertain instant, a value of a current force acting on the motor vehiclepart from the pulse signal, to use the value of the current force actingon the motor vehicle part as a criteria in determining whether theelectric motor is turned off or is reversed, and wherein the controlunit is adapted to use measured values of at least one motorcharacteristic taken on the electric motor before connection of theelectric motor to the motor vehicle part in determining the value of thecurrent force.
 14. Drive device as set forth in claim 13, wherein thecontrol unit is adapted to calculate a force change value (<F[k]), atthe instant each pulse signal is received by the control unit, frompreviously determined values of current force by determining arespective value which is indicative of the change of the motor rpm (<N*[k]), and by multiplying the respective value which is indicative of thechange of the motor rpm value with a proportionality factor (Vf) todetermine the instantaneous current force acting on the motor vehiclepart.